Pneumatic Tire

ABSTRACT

The pneumatic tire includes: a belt layer, a belt reinforcing layer, a tread portion, sidewall portions, a rim cushion rubber, and an electrically conductive rubber disposed in the rim cushion rubber and includes a first end in contact with a rim and exposed on an outer surface of the rim cushion rubber and a second end in contact with a tire component adjacent to the rim cushion rubber. The electrical resistance value of the electrically conductive rubber and a portion of the tread portion is 1×10 6  Ω or less. The electrical resistance value of the tire component, a coating rubber of the belt layer, and a coating rubber of the belt reinforcing layer is from 1×10 6  Ω to 1×10 8  Ω. The electrical resistance value of the rim cushion rubber and a side rubber of the sidewall portions is 1×10 8  Ω or greater.

TECHNICAL FIELD

This technology relates to a pneumatic tire capable of achieving goodrolling resistance reduction performance, high-speed durabilityperformance, and electrical resistance reduction performance in acompatible manner.

BACKGROUND ART

An example of a conventional pneumatic tire is described in JapaneseUnexamined Patent Application Publication No. 2009-023504A. Thepneumatic tire includes a tread portion, a sidewall portion, a beadportion, a carcass extending from the tread portion to the bead portionthrough the sidewall portion, and a breaker disposed at an outside ofthe carcass in a tire radial direction, wherein each of a tread rubber,a breaker rubber, and a sidewall rubber formed on the tread portion, thebreaker, and the sidewall portion, respectively, has a volumeresistivity of 1×10⁸ Ω ·cm or greater. The pneumatic tire furtherincludes an electrically conductive rubber disposed between a carcassply forming the carcass and the sidewall rubber and between the breakerand the tread portion and having a thickness of from 0.2 mm to 3.0 mm,an electrically conducting rubber contacting the electrically conductiverubber and embedded in the tread portion so as to be partially exposedon a surface of the tread portion, and a clinch connected to a lower endof the electrically conductive rubber and disposed in a region of thebead portion in contact with a rim flange. The electrically conductiverubber, the electrically conducting rubber and a clinch rubber has avolume resistivity of less than 1×10⁸ Ω·cm.

The pneumatic tire of Japanese Unexamined Patent Application PublicationNo. 2009-023504A described above has the object of effectivelydischarging static electricity generated when the pneumatic tire runs ona road surface while keeping the rolling resistance of the tire low. Thepneumatic tire of Japanese Unexamined Patent Application Publication No.2009-023504A includes an electrically conductive rubber disposed betweena carcass ply forming the carcass and the sidewall rubber and betweenthe breaker and the tread portion and having a thickness of from 0.2 mmto 3.0 mm, and a clinch connected to a lower end of the electricallyconductive rubber and disposed in a region of the bead portion incontact with a rim flange. The electrically conductive rubber and theclinch have a volume resistivity of less than 1×10⁸ Ω·cm. In otherwords, in the pneumatic tire of Japanese Unexamined Patent ApplicationPublication No. 2009-023504A, the electrically conductive rubberdisposed between the carcass ply and the sidewall rubber and between thebreaker and the tread portion, and clinch rubber disposed in the regionof the bead portion in contact with the rim flange are made of rubbermaterial with low electrical resistance. As a result, the rubbermaterial with low electrical resistance has high heat build-up, so ittends to reduce rolling resistance reduction performance and high-speeddurability performance.

SUMMARY

The present technology provides a pneumatic tire capable of achievinggood rolling resistance reduction performance, high-speed durabilityperformance, and electrical resistance reduction performance in acompatible manner.

A pneumatic tire according to a first aspect of the present technologycomprises:

a tread portion that comes into contact with a road surface, disposedexposed on an outermost side in a tire radial direction;

a belt layer disposed inward of the tread portion in the tire radialdirection;

a belt reinforcing layer disposed outward of at least a portion of thebelt layer in the tire radial direction;

sidewall portions disposed exposed on outermost sides in a tire widthdirection;

a rim cushion rubber disposed where bead portions come into contact witha rim; and

an electrically conductive rubber disposed in the rim cushion rubberincluding

a first end in contact with the rim exposed on an outer surface of therim cushion rubber, and

a second end in contact with a tire component adjacent to the rimcushion rubber; wherein

an electrical resistance value of the electrically conductive rubber anda portion of the tread portion is 1×10⁶ Ωor less;

an electrical resistance value of the tire component, a coating rubberof the belt layer, and a coating rubber of the belt reinforcing layer isfrom 1×10⁶ Ωto 1×10⁸ Ω; and

an electrical resistance value of the rim cushion rubber and a siderubber of the sidewall portions is 1×10⁸ Ω or greater.

According to this pneumatic tire, by including the electricallyconductive rubber with a lower electrical resistance value than that ofthe rim cushion rubber, electricity that enters from the rim flowstoward the tread portion through the electrically conductive rubber andthe tire component. Because of this, a low heat build-up rubber can beused without taking into consideration the electrical resistance valueof the rim cushion rubber, and thus rolling resistance reductionperformance and high-speed durability performance can be improved. As aresult, good rolling resistance reduction performance, high-speeddurability performance, and electrical resistance reduction performancecan be achieved in a compatible manner.

According to the pneumatic tire, the electricity from the rim flows invia the electrically conductive rubber and out to the road surface via aportion of the tread portion. These portions are most important factorsin electrical resistance value reduction. As such, by setting theelectrical resistance value to 1×10⁶ Ω or less, an effect of improvementin electrical resistance reduction performance can be significantlyobtained. Additionally, the tire component, the coating rubber of thebelt layer, and the coating rubber of the belt reinforcing layer formthe path through which electricity flows from the electricallyconductive rubber to a portion of the tread portion. These portions havegood rolling resistance reduction performance and electrical resistancevalue reduction in a compatible manner. As such, by setting theelectrical resistance value to from 1×10⁶ Ω to 1×10⁸ Ω, good rollingresistance reduction performance and electrical resistance reductionperformance can be significantly obtained in a compatible manner.Additionally, the rim cushion rubber and the side rubber of the sidewallportion are portions that factor into rolling resistance reductionperformance and high-speed durability performance. As such, by settingthe electrical resistance value to 1×10⁸ Ω or greater, an effect ofimprovement in rolling resistance reduction performance and high-speeddurability performance can be significantly obtained.

A pneumatic tire according to a second aspect of the present technologyis the first aspect further comprising a belt edge cushion rubberdisposed inward of an end portion of the belt layer in the tire radialdirection; wherein the belt edge cushion rubber has an electricalresistance value of from 1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire in which the belt edge cushion rubberis disposed, the belt edge cushion rubber forms the path through whichelectricity flows from the electrically conductive rubber to a portionof the tread portion. This portion has good rolling resistance reductionperformance and electrical resistance value reduction in a compatiblemanner. As such, by setting the electrical resistance value to from1×10⁶ Ω to 1×10⁸ Ω, good rolling resistance reduction performance andelectrical resistance reduction performance can be significantlyobtained in a compatible manner.

A pneumatic tire according to a third aspect of the present technologyis the first or second aspect, wherein

the tread portion includes a cap tread rubber exposed on a treadsurface, and an undertread rubber disposed inward of the cap treadrubber in the tire radial direction adjacent to the belt layer or thebelt reinforcing layer; and

the cap tread rubber has an electrical resistance value of 1×10⁶ Ω orless, and the undertread rubber has an electrical resistance value offrom 1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire, a portion of the tread portion isformed as part of the cap tread rubber as an outlet for electricity toflow to the road surface. By setting the electrical resistance value ofthe cap tread rubber, a most important portion in terms of electricalresistance value reduction, to 1×10⁶ Ω or less, an effect of improvementin electrical resistance reduction performance can be significantlyobtained. Additionally, the undertread rubber forms the path throughwhich electricity flows from the electrically conductive rubber to thecap tread rubber. This portion has good rolling resistance reductionperformance and electrical resistance value reduction in a compatiblemanner. As such, by setting the electrical resistance value of theundertread rubber to from 1×10⁶ Ω to 1×10⁸ Ω, good rolling resistancereduction performance and electrical resistance reduction performancecan be significantly obtained in a compatible manner.

A pneumatic tire according a fourth aspect of the present technology isthe first or second aspect, wherein

the tread portion includes a cap tread rubber exposed on a treadsurface, and an undertread rubber disposed inward of the cap treadrubber in the tire radial direction adjacent to the belt layer or thebelt reinforcing layer;

in the tread portion, an earth tread rubber is disposed passing throughthe cap tread rubber and the undertread rubber, the earth tread rubberincluding a first end exposed on the tread surface and a second end incontact with the belt layer or the belt reinforcing layer; and

the earth tread rubber has an electrical resistance value of 1×10⁶ Ω orless, and the cap tread rubber and the undertread rubber have anelectrical resistance value of 1×10⁸ Ω or greater.

According to this pneumatic tire, a portion of the tread portion isformed as part of the earth tread rubber as an outlet for electricity toflow to the road surface. By setting the electrical resistance value ofthe earth tread rubber, a most important portion in terms of electricalresistance value reduction, to 1×10⁶ Ω or less, an effect of improvementin electrical resistance reduction performance can be significantlyobtained. Additionally, by disposing the earth tread rubber, the captread rubber and the undertread rubber can be rendered as portions thatfactor into rolling resistance reduction performance and high-speeddurability performance. As such, by setting the electrical resistancevalue to 1×10⁸ Ω or greater, an effect of improvement in rollingresistance reduction performance and high-speed durability performancecan be significantly obtained.

A pneumatic tire according to a fifth aspect is any one of the first tofourth aspects, wherein

the tire component is a carcass layer reaching both of the bead portionsin the tire width direction and extending in a tire circumferentialdirection; and

a coating rubber of the carcass layer has an electrical resistance valueof from 1×10⁶ Ω to 10⁸ Ω.

According to this pneumatic tire, the end portions of the carcass layerin the tire width direction are folded over the pair of bead cores frominward to outward in the tire width direction, and the carcass layer isstretched in a toroidal shape in the tire circumferential direction toform the framework of the tire. By disposing the second end of theelectrically conductive rubber in contact with this carcass layer,electricity that enters from the rim can be appropriately guided to thetread portion side, and thus an effect of significant improvement in theelectrical resistance reduction performance can be obtained. The carcasslayer with such a configuration is suitable for forming the path throughwhich electricity flows from the electrically conductive rubber to aportion of the tread portion. This portion has good rolling resistancereduction performance and electrical resistance value reduction in acompatible manner. As such, by setting the electrical resistance valueof the coating rubber of the carcass layer to from 1×10⁶ Ω to 1×10⁸ Ω,good rolling resistance reduction performance and electrical resistancereduction performance can be significantly obtained in a compatiblemanner.

A pneumatic tire according a sixth aspect is any one of the first tofourth aspects, wherein

the tire component is an innerliner layer disposed on a tire innersurface; and

a rubber of the innerliner layer has an electrical resistance value offrom 1×10⁶ Ωto 10⁸ Ω.

According to this pneumatic tire, the innerliner layer is formed alongthe tire inner surface by disposing the end portions of the innerlinerlayer in the tire width direction at the lower portions of the beadcores of the pair of bead portions and stretching the innerliner layerin a toroidal shape in the tire circumferential direction. By disposingthe second end of the electrically conductive rubber in contact with theinnerliner layer, electricity that enters from the rim can beappropriately guided to the tread portion side, and thus an effect ofsignificant improvement in electrical resistance reduction performancecan be obtained. The innerliner layer with such a configuration issuitable for forming the path through which electricity flows from theelectrically conductive rubber to a portion of the tread portion. Thisportion has good rolling resistance reduction performance and electricalresistance value reduction in a compatible manner. As such, by settingthe electrical resistance value of the rubber of the innerliner layer tofrom 1×10⁶ Ω to 1×10⁸ Ω, good rolling resistance reduction performanceand electrical resistance reduction performance can be significantlyobtained in a compatible manner.

A pneumatic tire according to a seventh aspect is any one of the firstto fourth aspects, wherein

the tire component is a bead filler provided in the bead portions; and

a rubber of the bead filler has an electrical resistance value of from1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire in which the bead filler is the tirecomponent, the bead filler forms the path through which electricityflows from the electrically conductive rubber to a portion of the treadportion. This portion has good rolling resistance reduction performanceand electrical resistance value reduction in a compatible manner. Assuch, by setting the electrical resistance value of the rubber of thebead filler to from 1×10⁶ Ω to 1×10⁸ Ω, good rolling resistancereduction performance and electrical resistance reduction performancecan be significantly obtained in a compatible manner.

The pneumatic tire according to an eighth aspect is any one of the firstto fourth aspects, wherein

the tire component is a bead reinforcing layer provided in the beadportions; and

a coating rubber of the bead reinforcing layer has an electricalresistance value of from 1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire in which the bead reinforcing layer isthe tire component, the bead reinforcing layer forms the path throughwhich electricity flows from the electrically conductive rubber to aportion of the tread portion. This portion has good rolling resistancereduction performance and electrical resistance value reduction in acompatible manner. As such, by setting the electrical resistance valueof the coating rubber of the bead reinforcing layer to from 1×10⁶ Ω to1×10⁸ Ω, good rolling resistance reduction performance and electricalresistance reduction performance can be significantly obtained in acompatible manner.

The pneumatic tire according to the present technology can exhibit goodrolling resistance reduction performance, high-speed durabilityperformance, and electrical resistance reduction performance in acompatible manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 2 is a meridian cross-sectional view of the pneumatic tireaccording to the embodiment of the present technology.

FIG. 3 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 4 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 5 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 6 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 7 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 8 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 9 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 10 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 11 is a graph showing the pressure applied to a bead portion whenthe pneumatic tire is assembled on a rim.

FIG. 12 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 13 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 14 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 15 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 16 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 17 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 18 is an enlarged view of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

FIG. 19 is a table showing results of performance tests on pneumatictires according to examples of the present technology.

DETAILED DESCRIPTION

An embodiment of the present technology is described in detail belowwith reference to the drawings. However, the present technology is notlimited by the embodiment. Furthermore, components of the embodimentinclude components that may be easily replaced by those skilled in theart or that are substantially identical to components of the embodiment.Furthermore, modified examples of the embodiment may be combined asdesired within the scope apparent to those skilled in the art.

FIGS. 1 and 2 are meridian cross-sectional views of a pneumatic tireaccording to the present embodiment.

In the following description, “tire radial direction” refers to thedirection orthogonal to the rotational axis (not illustrated) of apneumatic tire 1. “Inward in the tire radial direction” refers to thedirection toward the rotational axis in the tire radial direction, and“outward in the tire radial direction” refers to the direction away fromthe rotational axis in the tire radial direction. “Tire circumferentialdirection” refers to the rotation direction taking the rotational axisas a center axis. In addition, “tire width direction” refers to thedirection parallel to the rotational axis. “Inward in the tire widthdirection” refers to the direction toward a tire equatorial plane CL(tire equatorial line) in the tire width direction, and “outward in thetire width direction” refers to the direction away from the tireequatorial plane CL in the tire width direction. “Tire equatorial planeCL” refers to a plane that is orthogonal to the rotational axis of thepneumatic tire 1 and that passes through the center of the pneumatictire 1 in the tire width direction. “Tire width” is a width in the tirewidth direction between components located outward in the tire widthdirection, or in other words, the distance between the components thatare most distant from the tire equatorial plane CL in the tire widthdirection. “Tire equatorial line” refers to a line along the tirecircumferential direction of the pneumatic tire 1 that lies on the tireequatorial plane CL. In the present embodiment, the tire equatorial lineis denoted by CL which is the same reference sign as that of the tireequatorial plane.

As illustrated in FIGS. 1 and 2, the pneumatic tire 1 of the presentembodiment includes a tread portion 2, shoulder portions 3 on oppositesides of the tread portion 2, and sidewall portions 4 and bead portions5 continuing in that order from the shoulder portions 3. The pneumatictire 1 also includes a carcass layer 6, a belt layer 7, a beltreinforcing layer 8, and an innerliner layer 9.

The tread portion 2 is made of tread rubber 2A, is exposed on theoutermost side of the pneumatic tire 1 in the tire radial direction, andthe surface thereof constitutes the contour of the pneumatic tire 1. Atread surface 21 is formed on an outer peripheral surface of the treadportion 2, in other words, on a road contact surface that comes incontact with a road surface when traveling. The tread surface 21 isprovided with a plurality (four in the present embodiment) of maingrooves 22 that extend in the tire circumferential direction. The maingrooves 22 are straight main grooves parallel to the tire equatorialline CL. Moreover, a plurality of rib-like land portions 23 that extendin the tire circumferential direction are formed in the tread surface21, defined by the plurality of main grooves 22. Note that the maingrooves 22 may extend in the tire circumferential direction in a bendingor curving manner. Additionally, lug grooves 24 that extend in adirection that intersects the main grooves 22 are provided in the landportions 23 of the tread surface 21. In the present embodiment, the luggrooves 24 show in the outermost land portions 23 in the tire widthdirection. The lug grooves 24 may meet the main grooves 22.Alternatively, the lug grooves 24 may have one end that does not meetthe main grooves 22 and terminates within a land portion 23. Inembodiments in which both ends of the lug grooves 24 meet the maingrooves 22, the land portions 23 are formed into a plurality ofblock-like land portions divided in the tire circumferential direction.Note that the lug grooves 24 may extend inclined with respect to thetire circumferential direction in a bending or curving manner.

The shoulder portions 3 are regions of the tread portion 2 locatedoutward in the tire width direction. In other words, the shoulderportions 3 are made of the tread rubber 2A. Additionally, the sidewallportions 4 are exposed on the outermost sides of the pneumatic tire 1 inthe tire width direction. The sidewall portions 4 are each made of aside rubber 4A. As illustrated in FIG. 1, an outer end portion of theside rubber 4A in the tire radial direction is disposed inward of an endportion of the tread rubber 2A in the tire radial direction. An innerend portion of the side rubber 4A in the tire radial direction isdisposed outward of an end portion of a rim cushion rubber 5A describedbelow in the tire width direction. Additionally, as illustrated in FIG.2, the outer end portion of the side rubber 4A in the tire radialdirection may be disposed outward of the end portion of the tread rubber2A in the tire radial direction and extend to the shoulder portion 3.The bead portions 5 each include a bead core 51 and a bead filler 52.The bead core 51 is formed by a bead wire, which is a steel wire, woundinto an annular shape. The bead filler 52 is a rubber material that isdisposed in space formed by an end of the carcass layer 6 in the tirewidth direction folded back at the position of the bead core 51. Thebead portions 5 each include an outwardly exposed rim cushion rubber 5Athat comes into contact with a rim R (illustrated by a long dasheddouble-short dashed line in FIGS. 3 to 8). The rim cushion rubber 5Aconstitutes the outer periphery of the bead portion 5. The rim cushionrubber 5A extends from the inner side of the bead portion 5 to the outerside of the bead portion 5 (sidewall portion 4) via the lower endportion of the bead portion 5 so as to cover the bead filler 52. Notethat in FIGS. 3 to 8, when the pneumatic tire 1 is mounted to the rim R,the rim cushion rubber 5A presses against the rim R at a radially innerportion of a bead toe portion located inward of the bead portion 5, anddeforms.

The end portions of the carcass layer 6 in the tire width direction arefolded over the pair of bead cores 51 from inward to outward in the tirewidth direction, and the carcass layer 6 is stretched in a toroidalshape in the tire circumferential direction to form the framework of thetire. The carcass layer 6 is constituted by a plurality ofcoating-rubber-covered carcass cords (not illustrated) disposed inalignment at an angle with respect to the tire circumferential directionthat conforms with the tire meridian direction. The carcass cords aremade of organic fibers (e.g., polyester, rayon, nylon, or the like). Atleast one carcass layer 6 is provided. Note that in FIGS. 1 and 2, thefolded end portion of the carcass layer 6 is provided covering the wholebead filler 52. However the folded end portion may be provided coveringthe bead filler 52 partially, so that the bead filler 52 is in contactwith the rim cushion rubber 5A (see FIG. 5). Additionally, a beadreinforcing layer 10 (see FIG. 6), which includes cord-rubber-coatedsteel cords or organic fibers (polyester, rayon, nylon, or the like),may be disposed between the outer folded end portion of the carcasslayer 6 in the tire width direction and the rim cushion rubber 5A.

The belt layer 7 has a multi-layer structure in which at least twolayers (belts 71 and 72) are layered. In the tread portion 2, the beltlayer 7 is disposed outward of the carcass layer 6 in the tire radialdirection on the outer periphery thereof and covers the carcass layer 6in the tire circumferential direction. The belts 71 and 72 each includea plurality of coating-rubber-covered cords (not illustrated) disposedin alignment at a predetermined angle with respect to the tirecircumferential direction (for example, from 20 degrees to 30 degrees).The cords are made of steel or organic fibers (polyester, rayon, nylon,or the like). Additionally, the belts 71 and 72 overlap each other andare disposed so that the direction of the cords of the respective beltsintersect each other. Additionally, as illustrated in FIG. 2, inembodiments in which the outer end portion of the side rubber 4A in thetire radial direction is disposed outward of the end portion of thetread rubber 2A in the tire radial direction and extends to the shoulderportion 3, a belt edge cushion rubber 7A is disposed inward of the endportion of the belt layer 7 (belt 71) in the tire radial direction andbetween this end portion and the carcass layer 6.

The belt reinforcing layer 8 is disposed outward of the belt layer 7 inthe tire radial direction on the outer periphery thereof and covers thebelt layer 7 in the tire circumferential direction. The belt reinforcinglayer 8 includes a plurality of coating-rubber-covered cords (notillustrated) disposed in alignment in the tire width directionsubstantially parallel (±5 degrees) to the tire circumferentialdirection. The cords are made of steel or organic fibers (polyester,rayon, nylon, or the like). The belt reinforcing layer 8 illustrated inFIGS. 1 and 2 is disposed so as to cover all of the belt layer 7 and tocover, in a multi-layered manner, end portions of the belt layer 7 inthe tire width direction. The configuration of the belt reinforcinglayer 8 is not limited to that described above. While not illustrated inthe drawings, a configuration may be used in which, for example, twolayers are disposed so as to cover all of the belt layer 7 or to coveronly the end portions of the belt layer 7 in the tire width direction.Additionally, while not illustrated in the drawings, a configuration ofthe belt reinforcing layer 8 may be used in which, for example, onelayer is disposed so as to cover all of the belt layer 7 or to coveronly the end portions of the belt layer 7 in the tire width direction.In other words, the belt reinforcing layer 8 overlaps at least the endportion of the belt layer 7 in the tire width direction. Additionally,the belt reinforcing layer 8 is constituted of a band-like stripmaterial (having, for example, a width of 10 mm) wound in the tirecircumferential direction.

The innerliner layer 9 is the tire inner surface, that is, the innerperipheral surface of the carcass layer 6. Both ends of the innerlinerlayer 9 in the tire width direction reach the bead cores 51 of the beadportions 5 and extend in the tire circumferential direction in atoroidal shape. The innerliner layer 9 prevents air molecules fromescaping from the tire. Note that, as illustrated in FIGS. 1 and 2, theinnerliner layer 9 may be disposed extending to lower portions of thebead cores 51 (inward in the tire radial direction). However, asillustrated in FIGS. 8 and 12, the innerliner layer 9 may be disposedextending to a position on the tire inner side of the bead portion 5near to the bead core 51.

FIGS. 3 to 8 are enlarged views of a main part of the pneumatic tireillustrated in FIGS. 1 and 2.

In the pneumatic tire 1 described above, as illustrated in FIGS. 3 to 8,the rim cushion rubber 5A is provided with an electrically conductiverubber 11. The electrically conductive rubber 11 is disposed in the rimcushion rubber 5A and includes a first end 11 a and a second end 11 b.The first end 11 a is a portion in contact with the rim R exposed on theouter surface of the rim cushion rubber 5A. The second end 11 b isprovided in contact with a tire component adjacent to the rim cushionrubber 5A. Additionally, the electrically conductive rubber 11 is madeof a rubber material with a lower electrical resistance value than thatof the rim cushion rubber 5A. The electrically conductive rubber 11 maybe provided continuously and may be provided intermittently in the tirecircumferential direction.

“Tire component adjacent to the rim cushion rubber 5A” refers to thecarcass layer 6 in FIGS. 3 and 8, the innerliner layer 9 in FIGS. 4 and7, the bead filler 52 in FIG. 5, and the bead reinforcing layer 10 inFIG. 6.

Note that the electrically conductive rubber 11 as illustrated in FIGS.3 to 8 is provided in contact with the tire component adjacent to therim cushion rubber 5A. However, the electrically conductive rubber 11may be in contact with a plurality of tire components in order to enablea more significant effect of guiding the electricity that enters fromthe rim R to the tread portion 2 side through the electricallyconductive rubber 11 and the tire component. Additionally, positioningthe conductive rubber 11 so that the first end 11 a is exposed on theouter surface of the rim cushion rubber 5A and the second end 11 b is incontact with the tire component adjacent to the rim cushion rubber 5Awith the distance between the first end 11 a and the second end 11 bbeing the shortest distance possible is preferable from the point ofview of obtaining a more significant effect of guiding the electricitythat enters from the rim R to the tread portion 2 side through theconductive rubber 11 and the tire component.

The tread portion 2 of the pneumatic tire 1 of the present embodiment isconfigured as illustrated in FIGS. 9 to 10, which are enlarged views ofa main part of the pneumatic tire 1 illustrated in FIGS. 1 and 2.

Here, as illustrated in FIG. 9, the tread rubber 2A which constitutesthe tread portion 2 includes a cap tread rubber 2Aa exposed on the treadsurface 21, and an undertread rubber 2Ab disposed inward of the captread rubber 2Aa in the tire radial direction and adjacent to the beltreinforcing layer 8 or the belt layer 7.

Additionally, as illustrated in FIG. 10, the tread portion 2 includes anearth tread rubber 12 as a part thereof. The earth tread rubber 12passes through the cap tread rubber 2Aa and the undertread rubber 2Ab ofthe tread portion 2 and includes a first end 12 a that is exposed on thetread surface 21 that is the outer surface of the tread portion 2, and asecond end 12 b that is disposed in contact with the belt reinforcinglayer 8 or the belt layer 7.

A pneumatic tire 1 with such a configuration includes: the belt layer 7,the belt reinforcing layer 8, the tread portion 2, the sidewall portion4, the rim cushion rubber 5A disposed where the bead portion 5 and therim R come into contact, and the electrically conductive rubber 11disposed in the rim cushion rubber 5A and includes a first end 11 a incontact with the rim R and exposed on the outer surface of the rimcushion rubber 5A and a second end 11 b in contact with a tire componentadjacent to the rim cushion rubber 5A. The electrical resistance valueof the electrically conductive rubber 11 and a portion of the treadportion 2 is 1×10⁶ Ω or less. The electrical resistance value of thetire component, the coating rubber of the carcass layer 6, the coatingrubber of the belt layer 7, and the coating rubber of the beltreinforcing layer 8 is from 1×10⁶ Ω to 1>10⁸ Ω. The electricalresistance value of the rim cushion rubber 5A and the side rubber 4A ofthe sidewall portion 4 is 1×10⁸ Ω or greater.

According to this pneumatic tire 1, by including the electricallyconductive rubber 11 with a lower electrical resistance value than therim cushion rubber 5A, electricity that enters from the rim R flowstoward the tread portion 2 through the electrically conductive rubber 11and the tire component. Because of this, a low heat build-up rubber canbe used without taking into consideration the electrical resistancevalue of the rim cushion rubber 5A, and thus rolling resistancereduction performance and high-speed durability performance can beimproved. As a result, good rolling resistance reduction performance,high-speed durability performance, and electrical resistance reductionperformance can be achieved in a compatible manner.

According to the pneumatic tire 1, the electricity from the rim R flowsin via the electrically conductive rubber 11 and out to the road surfacevia a portion of the tread portion 2. These portions are most importantfactors in electrical resistance value reduction. As such, by settingthe electrical resistance value to 1×10⁶ Ω or less, an effect ofimprovement in electrical resistance reduction performance can besignificantly obtained. Additionally, the tire component, the coatingrubber of the belt layer 7, and the coating rubber of the beltreinforcing layer 8 form the path through which electricity flows fromthe electrically conductive rubber 11 to a portion of the tread portion2. These portions have good rolling resistance reduction performance andelectrical resistance value reduction in a compatible manner. As such,by setting the electrical resistance value to from 1×10⁶ Ω to 1×10⁸ Ω,good rolling resistance reduction performance and electrical resistancereduction performance can be significantly obtained in a compatiblemanner. Additionally, the rim cushion rubber 5A and the side rubber 4Aof the sidewall portion 4 are portions that factor into rollingresistance reduction performance and high-speed durability performance.As such, by setting the electrical resistance value to 1×10⁸ Ω orgreater, an effect of improvement in rolling resistance reductionperformance and high-speed durability performance can be significantlyobtained.

Additionally, in the pneumatic tire 1 of the present embodiment, thebelt edge cushion rubber 7A is disposed inward of the end portion of thebelt layer 7 in the tire radial direction and has an electricalresistance value of from 1×10⁶ Ω to 1×10⁸ Ω.

According to the pneumatic tire 1 according to embodiments in which thebelt edge cushion rubber 7A is disposed, the belt edge cushion rubber 7Aforms the path through which electricity flows from the electricallyconductive rubber 11 to a portion of the tread portion 2. This portionhas good rolling resistance reduction performance and electricalresistance value reduction in a compatible manner. As such, by settingthe electrical resistance value to from 1×10⁶ Ω to 1×10⁸ Ω, good rollingresistance reduction performance and electrical resistance reductionperformance can be significantly obtained in a compatible manner.

Additionally, in the pneumatic tire 1 of the present embodiment, thetread portion 2 includes the cap tread rubber 2Aa exposed on the treadsurface 21 and the undertread rubber 2Ab disposed inward of the captread rubber 2Aa in the tire radial direction adjacent to the belt layer7 or the belt reinforcing layer 8. The cap tread rubber 2Aa has anelectrical resistance value of 1×10⁶ Ω or less. The undertread rubber2Ab has an electrical resistance value of from 1×10⁶ Ω to 1×10⁸ Ω.

According to the pneumatic tire 1, a portion of the tread portion 2 isformed as part of the cap tread rubber 2Aa as an outlet for electricityto flow to the road surface. By setting the electrical resistance valueof the cap tread rubber 2Aa, a most important portion in terms ofelectrical resistance value reduction, to 1×10⁶ Ω or less, an effect ofimprovement in electrical resistance reduction performance can besignificantly obtained. Additionally, the undertread rubber 2Ab formsthe path through which electricity flows from the electricallyconductive rubber 11 to the cap tread rubber 2Aa. This portion has goodrolling resistance reduction performance and electrical resistance valuereduction in a compatible manner. As such, by setting the electricalresistance value of the undertread rubber 2Ab to from 1×10⁶ Ω to 1×10⁸Ω, good rolling resistance reduction performance and electricalresistance reduction performance can be significantly obtained in acompatible manner.

Additionally, in the pneumatic tire 1 of the present embodiment, thetread portion 2 includes the cap tread rubber 2Aa exposed on the treadsurface 21 and the undertread rubber 2Ab disposed inward of the captread rubber 2Aa in the tire radial direction adjacent to the belt layer7 or the belt reinforcing layer 8. In the tread portion 2, the earthtread rubber 12 is provided passing through the cap tread rubber 2Aa andthe undertread rubber 2Ab. The first end 12 a of the earth tread rubber12 is exposed on the tread surface 21 and the second end 12 b isdisposed in contact with the belt layer 7 or the belt reinforcing layer8. The earth tread rubber 12 has an electrical resistance value of 1×10⁶Ω or less. The cap tread rubber 2Aa and the undertread rubber 2Ab havean electrical resistance value of 1×10⁸ Ω or greater.

According to the pneumatic tire 1, a portion of the tread portion 2 isformed as part of the earth tread rubber 12 as an outlet for electricityto flow to the road surface. By setting the electrical resistance valueof the earth tread rubber 12, a most important portion in terms ofelectrical resistance value reduction, to 1×10⁶ Ω or less, an effect ofimprovement in electrical resistance reduction performance can besignificantly obtained. Additionally, by disposing the earth treadrubber 12, the cap tread rubber 2Aa and the undertread rubber 2Ab can berendered as portions that factor into rolling resistance reductionperformance and high-speed durability performance. As such, by settingthe electrical resistance value to 1×10⁸ Ω or greater, an effect ofimprovement in rolling resistance reduction performance and high-speeddurability performance can be significantly obtained.

Additionally, in the pneumatic tire 1 of the present embodiment, thetire component is the carcass layer 6 reaching both bead portion 5 inthe tire width direction and extending in the tire circumferentialdirection. The electrical resistance value of the coating rubber of thecarcass layer 6 is from 1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire 1, the end portions of the carcasslayer 6 in the tire width direction are folded over the pair of beadcores 51 from in to out in the tire width direction, and the carcasslayer 6 is stretched in a toroidal shape in the tire circumferentialdirection to form the framework of the tire. By disposing the second end11 b of the electrically conductive rubber 11 in contact with thiscarcass layer 6, electricity that enters from the rim R can beappropriately guided toward the tread portion 2, and thus an effect ofsignificant improvement in the electrical resistance reductionperformance can be obtained. The carcass layer 6 with such aconfiguration is suitable for forming the path through which electricityflows from the electrically conductive rubber 11 to a portion of thetread portion 2 (cap tread rubber 2Aa or earth tread rubber 12). Thisportion has good rolling resistance reduction performance and electricalresistance value reduction in a compatible manner. As such, by settingthe electrical resistance value of the coating rubber of the carcasslayer 6 to from 1×10⁶ Ω to 1×10⁸ Ω, good rolling resistance reductionperformance and electrical resistance reduction performance can besignificantly obtained in a compatible manner.

Additionally, in the pneumatic tire 1 of the present embodiment, thetire component may be the innerliner layer 9 disposed on the tire innersurface. The electrical resistance value of the rubber of the innerlinerlayer 9 is from 1×10⁶ Ω to 1×10⁸ Ω.

According to this pneumatic tire 1, the innerliner layer 9 is formedalong the tire inner surface by disposing the end portions of theinnerliner layer 9 in the tire width direction at the lower portions ofthe bead cores 51 of the pair of bead portions 5 and stretching theinnerliner layer 9 in a toroidal shape in the tire circumferentialdirection. By disposing the second end 11 b of the electricallyconductive rubber 11 in contact with the innerliner layer 9, electricitythat enters from the rim R can be appropriately guided to the treadportion 2 side, and thus an effect of significant improvement inelectrical resistance reduction performance can be obtained. Theinnerliner layer 9 with such a configuration is suitable for forming thepath through which electricity flows from the electrically conductiverubber 11 to a portion of the tread portion 2 (cap tread rubber 2Aa orearth tread rubber 12). This portion has good rolling resistancereduction performance and electrical resistance value reduction in acompatible manner. As such, by setting the electrical resistance valueof the rubber of the innerliner layer 9 to from 1×10⁶ Ω to 1×10⁸ Ω, goodrolling resistance reduction performance and electrical resistancereduction performance can be significantly obtained in a compatiblemanner.

Additionally, in the pneumatic tire 1 of the present embodiment, thetire component may be the bead filler 52 provided in the bead portion 5.The electrical resistance value of the rubber of the bead filler 52 isfrom 1×10⁶ Ω to 1×10⁸ Ω.

According to the pneumatic tire 1 in which the bead filler 52 is thetire component, the bead filler 52 forms the path through whichelectricity flows from the electrically conductive rubber 11 to aportion of the tread portion 2 (cap tread rubber 2Aa or earth treadrubber 12). This portion has good rolling resistance reductionperformance and electrical resistance value reduction in a compatiblemanner. As such, by setting the electrical resistance value of therubber of the bead filler 52 to from 1×10⁶ Ω to 1×10⁸ Ω, good rollingresistance reduction performance and electrical resistance reductionperformance can be significantly obtained in a compatible manner.

Additionally, in the pneumatic tire 1 of the present embodiment, thetire component may be the bead reinforcing layer 10 provided in the beadportion 5. The electrical resistance value of the coating rubber of thebead reinforcing layer 10 is from 1×10⁶ Ω to 1×10⁸ Ω.

According to the pneumatic tire 1 in which the bead reinforcing layer 10is the tire component, the bead reinforcing layer 10 forms the paththrough which electricity flows from the electrically conductive rubber11 to a portion of the tread portion 2 (cap tread rubber 2Aa or earthtread rubber 12). This portion has good rolling resistance reductionperformance and electrical resistance value reduction in a compatiblemanner. As such, by setting the electrical resistance value of thecoating rubber of the bead reinforcing layer 10 to from 1×10⁶ Ω to 1×10⁸Ω, good rolling resistance reduction performance and electricalresistance reduction performance can be significantly obtained in acompatible manner.

As illustrated in FIGS. 4, 7, and 8, in the pneumatic tire 1 of thepresent embodiment, the first end 11 a of the electrically conductiverubber 11 is preferably disposed inward of a horizontal line H in thetire radial direction based on an inner end of the bead core 51 of thebead portion 5 in the tire radial direction, in a meridiancross-section.

The horizontal line H is orthogonal to the tire equatorial plane CL andparallel with the tire width direction when a cut sample with a meridiancross-section is fitted to the rim width of the regular rim describedbelow. Additionally, in FIGS. 4, 7, and 8, a range A-B is the range inwhich the bead portion 5 is in contact with the rim R when the pneumatictire 1 is assembled on the rim R. Within the range A-B, position C islocated inward of the end of the bead core 51 on the tire inner side inthe tire radial direction; position D is located inward of the end ofthe bead core 51 on the tire outer side in the tire radial direction;position E is located on the horizontal line H; position F is located onthe tire outer side of the outer side of the bead core 51 in the tireradial direction; and position G is an inflection point located on thetire outer side of the bead portion 5. FIG. 11 is a graph showing thepressure applied to the bead portion 5 at the positions within the rangeA-B when the pneumatic tire 1 is assembled on the rim R. Additionally,in FIG. 11, the solid line shows the pressure applied to the beadportion 5 when the vehicle is in a static state (when the vehicle isstop or traveling at low speeds). The dashed line shows the pressureapplied to the bead portion 5 when the vehicle is traveling at highspeeds (150 km/h or greater).

As illustrated in FIG. 11, in the range between position A, which isinward of the horizontal line H in the tire radial direction, andposition E, because the bead core 51 is wedged against the rim R, thecontact pressure with the rim R is great, and thus contact with the rimR is ensured even when traveling at high speeds. Accordingly, bydisposing the first end 11 a of the electrically conductive rubber 11inward in the tire radial direction of the horizontal line H, which isbased on the inner end of the bead core 51 in the tire radial direction,electrical resistance can be efficiently reduced and good rollingresistance reduction performance and high-speed durability performancecan be achieved in a compatible manner. Note that as illustrated in FIG.11, in the range from position F to position contact pressure with therim R is great when the vehicle is in a static state. However, when thevehicle is traveling at high speeds, the bead portion 5 is susceptibleto displacement originating at the bead core 51, and thus the contactpressure with the rim R tends to be decreased.

As illustrated in FIG. 12, which is an enlarged view of a main part ofthe pneumatic tire 1 illustrated in FIGS. 1 and 2, in the pneumatic tire1 of the present embodiment, the electrically conductive rubber 11 ispreferably disposed so that, in a meridian cross-section, the second end11 b is disposed in a ±45° range with respect to a normal line N to theprofile of the bead portion 5 at position P of the first end 11 a.

As illustrated in FIG. 12, position P of the first end 11 a is thecenter position of the first end 11 a in terms of width in the thicknessdirection when a cut sample with a meridian cross-section is fitted tothe rim width of the regular rim described below. The normal line N isorthogonal to a tangent line T at position P of the profile of the beadportion 5. By disposed the second end 11 b in a ±45° range with respectto the normal line N, the volume of the electrically conductive rubber11 is prevented by being too great. As a result, heat build-up issuppressed and rolling resistance reduction performance and high-speeddurability performance can be maintained.

As illustrated in FIGS. 13 to 18, which are enlarged views of a mainpart of the pneumatic tire 1 illustrated in FIGS. 1 and 2, in thepneumatic tire 1 of the present embodiment, the electrically conductiverubber 11 preferably has widths W1, W2, W3 in the thickness direction ina meridian cross-section of from 0.5 mm to 10.0 mm.

The width W1 is the maximum dimension between the first end 11 a and thesecond end 11 b of the electrically conductive rubber 11 (in embodimentswith a widening electrically conductive rubber 11), or the minimumdimension therebetween (in embodiments with a narrowing electricallyconductive rubber 11). The width W2 is the dimension of the first end 11a of the electrically conductive rubber 11. The width W3 is thedimension of the second end 11 b of the electrically conductive rubber11.

When the widths W1, W2, W3 of the electrically conductive rubber 11 havea minimum dimension of less than 0.5 mm, electrical resistance is low,and thus the electrical resistance reduction effect tends to bedecreased. When the widths W1, W2, W3 of the electrically conductiverubber 11 have a maximum dimension of greater than 10.0 mm, the volumeof the electrically conductive rubber 11 is great and thus the heatbuild-up is increased. As a result, rolling resistance reductionperformance and high-speed durability performance tend to be decreased.Accordingly, by the widths W1, W2, W3 of the electrically conductiverubber 11 being from 0.5 mm to 10.0 mm, good rolling resistancereduction performance, high-speed durability performance, and electricalresistance reduction performance are achieved in a compatible manner,and is thus preferable.

As illustrated in FIGS. 13 to 18, which are enlarged views of a mainpart of the pneumatic tire 1 illustrated in FIGS. 1 and 2, in thepneumatic tire 1 of the present embodiment, the electrically conductiverubber 11 preferably has widths W1, W2, W3 in the thickness direction ina meridian cross-section of from 0.5 mm to 6.0 mm.

When the widths W1, W2, W3 of the electrically conductive rubber 11 havea dimension of less than 0.5 mm, electrical resistance is low, and thusthe electrical resistance reduction effect tends to be decreased. By thewidths W1, W2, W3 of the electrically conductive rubber 11 having adimension of 6.0 mm or less, an increase in heat build-up is suppressedby the volume of the electrically conductive rubber 11 being preventedfrom being too large. Accordingly, by the widths W1, W2, W3 of theelectrically conductive rubber 11 being from 0.5 mm to 6.0 mm, goodrolling resistance reduction performance, high-speed durabilityperformance, and electrical resistance reduction performance areachieved in a compatible manner, and is thus more preferable.

FIG. 13 illustrates an embodiment in which the widths W1, W2, W3 of theelectrically conductive rubber 11 are equal from the first end 11 a tothe second end 11 b. FIG. 14 illustrates an embodiment in which theelectrically conductive rubber 11 widens to the width W1 at a positionbetween the first end 11 a to the second end 11 b. In the embodimentillustrated in FIG. 14, the width W2 of the first end 11 a and the widthW3 of the second end 11 b should be 0.5 mm or greater and the width W1at the widened position should be 10.0 mm or less (preferably 6.0 mm orless). In the embodiment illustrated in FIG. 14, the electricallyconductive rubber 11 is increased in width W1 at its middle portion.This allows electricity to flow easily and thus enables a significantelectrical resistance reduction effect to be obtained. FIG. 15illustrates an embodiment in which the width W2 of the first end 11 aand the width W3 of the second end 11 b are equal and greater than thewidth W1 at a position between the first end 11 a and the second end 11b. FIG. 16 illustrates an embodiment in which the electricallyconductive rubber 11 widens at the first end 11 a to the width W2. FIG.17 illustrates an embodiment in which the electrically conductive rubber11 widens at the second end l lb to the width W3. Additionally, FIG. 18illustrates an embodiment in which the width W2 of the first end 11 aand the width W3 of the second end 11 b are greater than the width W1 ata position between the first end 11 a and the second end 11 b, and thewidth W2 of the first end 11 a is greater than the width W3 of thesecond end 11 b. In the embodiments illustrated in FIGS. 15 to 18, thewidth W1 at a position between the first end 11 a and the second end 11b should be 0.5 mm or greater, and the width W2 of the first end 11 aand the width W3 of the second end 11 b should be 10.0 mm or less(preferably 6.0 mm or less). In the embodiments illustrated in FIGS. 15to 18, the width W2 of the first end 11 a and the width W3 of the secondend 11 b of the electrically conductive rubber 11 that is in contactwith the rim R side and the tire component side are greater than thewidth W1 at a position between the first end 11 a and the second end 11b. As a result, the flow of electricity in and out is improved due tothe greater contact area, and thus a significant electrical resistancereduction effect can be obtained. Furthermore, in the embodimentillustrated in FIG. 18, the width W2 of the first end 11 a and the widthW3 of the second end 11 b are greater than the width W1 at a positionbetween the first end 11 a and the second end 11 b, and the width W2 ofthe first end 11 a is greater than the width W3 of the second end 11 b.As a result, the flow of electricity in from the rim R side is improved,and thus a more significant electrical resistance reduction effect canbe obtained.

According to the pneumatic tire 1 of the present embodiment, in theelectrically conductive rubber 11, in a meridian cross-section, thewidth W2 of the first end 11 a in the thickness direction is preferablygreater than the maximum width W1 at a position between the first end 11a and the second end 11 b. Additionally, in the electrically conductiverubber 11, in a meridian cross-section, the width W3 of the second end11 b in the thickness direction is preferably greater than the maximumwidth W1 at a position between the first end 11 a and the second end 11b. Furthermore, in the electrically conductive rubber 11, in a meridiancross-section, the width W2 of the first end 11 a in the thicknessdirection is preferably greater than the width W3 of the second end 11b.

Additionally, in the pneumatic tire 1 of the present embodiment, theelectrically conductive rubber 11 is preferably disposed at a pluralityof positions.

By disposing the electrically conductive rubber 11 at a plurality ofpositions, a significant electrical resistance reduction effect can beobtained. By disposing at least the first end 11 a of the electricallyconductive rubber 11 in the range from position A to position E or inthe range from position F to position G where contact pressure with therim R is comparatively great as illustrated in FIG. 11, an electricalresistance reduction effect can be obtained, and is thus preferable. Inparticular, by disposing a plurality of the electrically conductiverubbers 11 at a plurality of positions so that at least the first ends11 a are disposed in the range from position A to position E wherecontact pressure with the rim R is great, an electrical resistancereduction effect can be obtained, and is thus more preferable.Furthermore, by disposing a plurality of the electrically conductiverubbers 11 at a plurality of positions so that at least the first ends11 a are disposed in the range from position C to position D, whichcorresponds to a lower portion of the bead core 51 (inward in the tireradial direction) where contact pressure with the rim R is great, anelectrical resistance reduction effect can be obtained, and is thus evenmore preferable.

Additionally, in the pneumatic tire 1 of the present embodiment, theloss tangent tan δ at 60° C. of the coating rubber of the carcass layer6 and the side rubber 4A of the sidewall portion 4 is preferably 0.12 orless. The electrical resistance value of the coating rubber of thecarcass layer 6 and the side rubber 4A of the sidewall portion 4 ispreferably 1×10⁷ Ω or greater. Note that the loss tangent tan δ at 60°C. is measured using a sample from the pneumatic tire 1.

According to this pneumatic tire 1, by defining the coating rubber ofthe carcass layer 6 and the side rubber 4A of the sidewall portion 4 asdescribed above, a low heat build-up rubber can be used as the coatingrubber of the carcass layer 6 and the side rubber 4A of the sidewallportion 4. As a result, the effect of significant improvement in rollingresistance reduction performance and the high-speed durabilityperformance can be obtained, and also an improvement in heat sagresistance performance, which is a factor in high-speed steeringstability performance, can be obtained.

EXAMPLES

In the examples, performance tests for electrical resistance reductionperformance using the tire electrical resistance value, rollingresistance reduction performance, and high-speed durability performance(with a camber applied) were performed on a plurality of types ofdifferent specifications (see FIG. 19).

The pneumatic tires (test tires) used in the performance tests had atire size of 235/45R19, were assembled on a regular rim of 19×8J, andwere inflated to the regular internal pressure (250 kPa).

Here, “regular rim” refers to a “standard rim” defined by the JapanAutomobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim”defined by the Tire and Rim Association, Inc. (TRA), or a “MeasuringRim” defined by the European Tyre and Rim Technical Organisation(ETRTO). “Regular internal pressure” refers to “maximum air pressure”defined by JATMA, a maximum value given in “tire load limits at variouscold inflation pressures” defined by TRA, or “inflation pressures”defined by ETRTO. “Regular load” refers to “maximum load capacity”defined by JATMA, a maximum value given in “tire load limits at variouscold inflation pressures” defined by TRA, or “load capacity” defined byETRTO.

For the evaluation of electrical resistance reduction performance, whichis the tire electrical resistance value, a voltage of 1000 V was appliedunder conditions of 23° C. temperature and 50% humidity and theresistance value between the tread surface and the rim was measured andexpressed as the electrical resistance value Ω. In the evaluation,smaller values indicate superior electrical discharge properties andsuperior electrical resistance reduction performance.

For the evaluation of rolling resistance reduction performance, thetires were put on an indoor drum testing machine, and the resistance ata speed of 50 km/h when loaded with 4 kN was measured. Then, themeasurement results were expressed as index values with the result ofthe conventional example being defined as the reference (100). In theevaluation, larger index values indicate less rolling resistance andthus superior rolling resistance reduction performance.

For the evaluation of high-speed durability performance, the test tireswere inflated to 120% the specified internal pressure and subjected todrying degradation for five days in an 80° C.-temperature environment.Thereafter, the test tires were imparted with specified internalpressure and put on a 1707-mm-diameter drum test machine with a camberapplied. The test was started at a speed of 120 km/h and a load of 5 kNapplied to the test tires. Every 24 hours, the speed was increased by 10km/h until the tire failed. The distance traveled until failure wasmeasured. The results were expressed as index values with the result ofthe conventional example being defined as the reference (100). In theevaluation, larger index values indicate superior high-speed durabilityperformance.

As indicated in FIG. 19, the pneumatic tire of the conventional exampleand the pneumatic tire of the comparative example do not include anelectrically conductive rubber. The pneumatic tire of the comparativeexample includes an earth tread rubber that passes through a cap treadrubber and an undertread rubber of a tread portion. The earth treadrubber includes a first end and a second end of identical width. Thefirst end is exposed on the tread surface. The second end is disposed incontact with a belt layer or a belt reinforcing layer. The pneumatictires of Working Examples 1 to 9 include the electrically conductiverubber illustrated in FIG. 8. The pneumatic tire of Working Example 10includes the electrically conductive rubber illustrated in FIG. 7. Thepneumatic tire of Working Example 11 includes the electricallyconductive rubber illustrated in FIG. 5. The pneumatic tire of WorkingExample 12 includes the electrically conductive rubber illustrated inFIG. 6. The pneumatic tires of Working Examples 1, 2, 5, and 6 include abelt edge cushion rubber. The pneumatic tires of Working Examples 1 to 4do not include an earth tread rubber. The pneumatic tires of WorkingExamples 5 to 12 include an earth tread rubber.

It can be seen from the test results indicated in FIG. 19 that thepneumatic tires of Working Examples 1 to 12 have good rolling resistancereduction performance, high-speed durability performance, and electricalresistance reduction performance, which is the tire electricalresistance value, in a compatible manner.

1. A pneumatic tire comprising: a tread portion that comes into contactwith a road surface, disposed exposed to an outermost side in a tireradial direction; a belt layer disposed inward of the tread portion inthe tire radial direction; a belt reinforcing layer disposed outward ofat least a portion of the belt layer in the tire radial direction;sidewall portions disposed exposed on outermost sides in a tire widthdirection; a rim cushion rubber disposed where bead portions come intocontact with a rim; and an electrically conductive rubber disposed inthe rim cushion rubber including a first end in contact with the rimexposed on an outer surface of the rim cushion rubber, and a second endin contact with a tire component adjacent to the rim cushion rubber;wherein an electrical resistance value of the electrically conductiverubber and a portion of the tread portion is 1×10⁶ Ω or less; anelectrical resistance value of the tire component, a coating rubber ofthe belt layer, and a coating rubber of the belt reinforcing layer isfrom 1×10⁶ Ω to 1×10⁸ Ω; and an electrical resistance value of the rimcushion rubber and a side rubber of the sidewall portions is 1×10⁸ Ω orgreater.
 2. The pneumatic tire according to claim 1, further comprisinga belt edge cushion rubber disposed inward of an end portion of the beltlayer in the tire radial direction; wherein the belt edge cushion rubberhas an electrical resistance value of from 1×10⁶ Ω to 1×10⁸ Ω.
 3. Thepneumatic tire according to claim 1, wherein the tread portion includesa cap tread rubber exposed on a tread surface, and an undertread rubberdisposed inward of the cap tread rubber in the tire radial directionadjacent to the belt layer or the belt reinforcing layer; and the captread rubber has an electrical resistance value of 1×10⁶ Ω or less, andthe undertread rubber has an electrical resistance value of from 1×10⁶ Ωto 1×10⁸ Ω.
 4. The pneumatic tire according to claim 1, wherein thetread portion includes a cap tread rubber exposed on a tread surface,and an undertread rubber disposed inward of the cap tread rubber in thetire radial direction adjacent to the belt layer or the belt reinforcinglayer; in the tread portion, an earth tread rubber is disposed passingthrough the cap tread rubber and the undertread rubber, the earth treadrubber including a first end exposed on the tread surface and a secondend in contact with the belt layer or the belt reinforcing layer; andthe earth tread rubber has an electrical resistance value of 1×10⁶ Ω orless, and the cap tread rubber and the undertread rubber have anelectrical resistance value of 1×10⁸ Ω or greater.
 5. The pneumatic tireaccording to claim 1, wherein the tire component is a carcass layerreaching both of the bead portions in the tire width direction andextending in a tire circumferential direction; and a coating rubber ofthe carcass layer has an electrical resistance value of from 1×10⁶ Ω to1×10⁸ Ω.
 6. The pneumatic tire according to claim 1, wherein the tirecomponent is an innerliner layer disposed on a tire inner surface; and arubber of the innerliner layer has an electrical resistance value offrom 1×10⁶ Ω to 1×10⁸ Ω.
 7. The pneumatic tire according to claim 1,wherein the tire component is a bead filler provided in the beadportions; and a rubber of the bead filler has an electrical resistancevalue of from 1×10⁶ Ω to 1×10⁸ Ω.
 8. The pneumatic tire according toclaim 1, wherein the tire component is a bead reinforcing layer providedin the bead portions; and a coating rubber of the bead reinforcing layerhas an electrical resistance value of from 1×10⁶ Ω to 10⁸ Ω.
 9. Thepneumatic tire according to claim 2, wherein the tread portion includesa cap tread rubber exposed on a tread surface, and an undertread rubberdisposed inward of the cap tread rubber in the tire radial directionadjacent to the belt layer or the belt reinforcing layer; and the captread rubber has an electrical resistance value of 1×10⁶ Ω or less, andthe undertread rubber has an electrical resistance value of from 1×10⁶ Ωto 1×10⁸ Ω.
 10. The pneumatic tire according to claim 2, wherein thetread portion includes a cap tread rubber exposed on a tread surface,and an undertread rubber disposed inward of the cap tread rubber in thetire radial direction adjacent to the belt layer or the belt reinforcinglayer; in the tread portion, an earth tread rubber is disposed passingthrough the cap tread rubber and the undertread rubber, the earth treadrubber including a first end exposed on the tread surface and a secondend in contact with the belt layer or the belt reinforcing layer; andthe earth tread rubber has an electrical resistance value of 1×10⁶ Ω orless, and the cap tread rubber and the undertread rubber have anelectrical resistance value of 1×10⁸ Ω or greater.
 11. The pneumatictire according to claim 2, wherein the tire component is a carcass layerreaching both of the bead portions in the tire width direction andextending in a tire circumferential direction; and a coating rubber ofthe carcass layer has an electrical resistance value of from 1×10⁶ Ω to1×10⁸ Ω.
 12. The pneumatic tire according to claim 2, wherein the tirecomponent is an innerliner layer disposed on a tire inner surface; and arubber of the innerliner layer has an electrical resistance value offrom 1×10⁶ Ω to 1×10⁸Ω.
 13. The pneumatic tire according to claim 2,wherein the tire component is a bead filler provided in the beadportions; and a rubber of the bead filler has an electrical resistancevalue of from 1×10⁶ Ω to 1×10⁸ Ω.
 14. The pneumatic tire according toclaim 2, wherein the tire component is a bead reinforcing layer providedin the bead portions; and a coating rubber of the bead reinforcing layerhas an electrical resistance value of from 1×10⁶ Ω to 10⁸ Ω.
 15. Thepneumatic tire according to claim 3, wherein the tire component is acarcass layer reaching both of the bead portions in the tire widthdirection and extending in a tire circumferential direction; and acoating rubber of the carcass layer has an electrical resistance valueof from 1×10⁶ Ω to 1×10⁸ Ω.
 16. The pneumatic tire according to claim 3,wherein the tire component is an innerliner layer disposed on a tireinner surface; and a rubber of the innerliner layer has an electricalresistance value of from 1×10⁶ Ω to 1×10⁸Ω.
 17. The pneumatic tireaccording to claim 3, wherein the tire component is a bead fillerprovided in the bead portions; and a rubber of the bead filler has anelectrical resistance value of from 1×10⁶ Ω to 1×10⁸ Ω.
 18. Thepneumatic tire according to claim 3, wherein the tire component is abead reinforcing layer provided in the bead portions; and a coatingrubber of the bead reinforcing layer has an electrical resistance valueof from 1×10⁶ Ω to 10⁸ Ω.